U.S. patent number 6,271,903 [Application Number 09/012,041] was granted by the patent office on 2001-08-07 for liquid crystal display device having a light shielding matrix.
This patent grant is currently assigned to LG. Philips LCD Co., Ltd.. Invention is credited to Hyunho Shin, Chae Gee Sung, Kouji Takashina.
United States Patent |
6,271,903 |
Shin , et al. |
August 7, 2001 |
Liquid crystal display device having a light shielding matrix
Abstract
A liquid crystal display device composed of: a first substrate
and a second substrates; a liquid crystal layer provided between
the first and second substrates; a plurality of pixel regions
provided on the surface opposing the second substrate of the first
substrate, each of which pixel regions has at least one pixel
electrode and a common electrode for cooperatively applying an
electric field in a direction along the surface of the first
substrate; and a conductive light shielding matrix provided on the
surface opposing the first substrate of the second substrate which
light shielding matrix has openings each corresponding to a display
region of each of the pixel regions and shades non-display regions
other than the pixel regions; in which the light shielding matrix
and the common electrode are set to substantially the same
voltage.
Inventors: |
Shin; Hyunho (Sendai,
JP), Sung; Chae Gee (Miyagi-ken, JP),
Takashina; Kouji (Miyagi-ken, JP) |
Assignee: |
LG. Philips LCD Co., Ltd.
(Seoul, KR)
|
Family
ID: |
11757315 |
Appl.
No.: |
09/012,041 |
Filed: |
January 22, 1998 |
Foreign Application Priority Data
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Jan 23, 1997 [JP] |
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9-010691 |
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Current U.S.
Class: |
349/110; 349/111;
349/141 |
Current CPC
Class: |
G02F
1/134363 (20130101); G02F 1/133512 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101); G02F 1/13 (20060101); G02F
1/1343 (20060101); G02F 001/133 () |
Field of
Search: |
;349/111,141,110 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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06-99939 |
|
Mar 1996 |
|
EP |
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6-160878 |
|
Jun 1994 |
|
JP |
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6-273803 |
|
Sep 1994 |
|
JP |
|
07-301814 |
|
Nov 1995 |
|
JP |
|
09-269504 |
|
Oct 1997 |
|
JP |
|
Other References
Matsumoto, et al., LP-A: Display Characteristics of
In-Plane-Switching (IPS) LCDs and a Wide-Viewing-Angle 14.5-in. IPS
TFT-LCD, Euro Display 96, 10/1-3/96, pp. 445-448..
|
Primary Examiner: Dudek; James A.
Attorney, Agent or Firm: Long Aldridge & Norman
Claims
What is claimed is:
1. A liquid crystal display device comprising:
a first substrate and a second substrate;
a liquid crystal layer provided between said first and second
substrates;
a plurality of pixel regions provided on the surface opposing said
second substrate of said first substrate, each of said pixel
regions comprising at least one pixel electrode and a common
electrode cooperatively applying an electric field in a direction
along the surface of said first substrate; and
a conductive light shielding matrix provided on the surface
opposing said first substrate of said second substrate, said light
shielding matrix having openings, each corresponding to a display
region of each of said pixel regions, and shading non-display
regions other than said pixel regions;
wherein said light shielding matrix and said common electrode are
set to substantially the same voltage,
wherein said common electrode formed on said first substrate is
extended to a peripheral edge of said first substrate, said light
shielding matrix formed on said second substrate is extended to a
peripheral edge of said second substrate, and said common electrode
and said light shielding matrix are electrically connected via
conductive member at the peripheral edge of said first and second
substrates.
2. A liquid crystal display device as set forth in claim 1, wherein
the voltage difference between said light shielding matrix and said
common electrode is set in a range of from -0.5 V to +0.5 V, both
inclusive.
3. A liquid crystal display device according to claim 1, wherein
the common electrode and the pixel electrode are on different
layers.
4. A liquid crystal display device according to claim 1, wherein
the light shielding matrix includes chromium.
5. A liquid crystal display device according to claim 1, wherein
the light shielding matrix includes chromium and chromium
oxide.
6. A liquid crystal display device according to claim 1, wherein
the light shielding matrix includes chromium oxide.
7. A liquid crystal display device comprising:
a first substrate and a second substrate;
a liquid crystal layer provided between said first and second
substrates;
a plurality of pixel regions provided on the surface opposing said
second substrate of said first substrate, each of said pixel
regions comprising at least one pixel electrode and a common
electrode cooperatively applying an electric field in a direction
along the surface of said first substrate; and
a conductive light shielding matrix provided on the surface
opposing said first substrate of said second substrate, said light
shielding matrix having openings each corresponding to a display
region of each of said pixel regions, and shading non-display
regions other than said pixel regions;
wherein said light shielding matrix and said common electrode are
set to substantially the same voltage,
wherein said liquid crystal layer is encapsulated between said
first and second substrates by a sealing member, said common
electrode formed on said first substrate is extended outside the
sealing position of said sealing member on said first substrate,
said light shielding matrix formed on said second substrate is
extended outside the sealing position of said sealing member on
said second substrate, and said common electrode and said light
shielding matrix are electrically connected at a position outside
said sealing member via a conductive member provided between said
first and second substrates.
8. A liquid crystal display device according to claim 7, wherein
the common electrode and the pixel electrode are on different
layers.
9. A liquid crystal display device according to claim 7, wherein
the light shielding matrix includes chromium.
10. A liquid crystal display device according to claim 7, wherein
the light shielding matrix includes chromium and chromium
oxide.
11. A liquid crystal display device according to claim 9, wherein
the light shielding matrix includes chromium oxide.
12. A liquid crystal display device as set forth in claim 7,
wherein the voltage difference between said light shielding matrix
and said common electrode is set in a range of from -0.5 V to +0.5
V, both inclusive.
13. A liquid crystal display device comprising:
a first substrate and a second substrate;
a liquid crystal layer provided between said first and second
substrates;
a plurality of pixel regions provided on the surface opposing said
second substrate of said first substrate, each of said pixel
regions comprising at least one pixel electrode and a common
electrode cooperatively applying an electric field in a direction
along the surface of said first substrate; and
a conductive light shielding matrix provided on the surface
opposing said first substrate of said second substrate, said light
shielding matrix having openings, each corresponding to a display
region of each of said pixel regions, and shading non-display
regions other than said pixel regions;
wherein a conductive film at substantially the same voltage as said
common electrode is formed at least above said light shielding
matrix with an insulating film interposed therebetween,
wherein said common electrode formed on said first substrate is
extended to a peripheral edge of said first substrate, said light
shielding matrix formed on said second substrate is extended to a
peripheral edge of said second substrate, and said common electrode
and said light shielding matrix are electrically connected via
conductive member at the peripheral edge of said first and second
substrates.
14. A liquid crystal display device as set forth in claim 13,
wherein the voltage difference between said conductive film and
said common electrode is set in a range of from -0.5 V to +0.5 V,
both inclusive.
15. A liquid crystal display device according to claim 13, wherein
the conductive film has an opening substantially the same size as
the opening in the light shielding matrix.
16. A liquid crystal display device according to claim 13, wherein
the conductive film includes a transparent layer.
17. A liquid crystal display device according to claim 13, wherein
the conductive film includes an opaque layer.
18. A liquid crystal display device according to claim 13, wherein
the conductive film is in a horizontal direction.
19. A liquid crystal display device according to claim 13, wherein
the conductive film is in a vertical direction.
20. A liquid crystal display device according to claim 13, wherein
the conductive film has a first portion in a first direction and a
second portion in a second direction is in a horizontal
direction.
21. A liquid crystal display device according to claim 13, wherein
the common electrode and the pixel electrode are on different
layers.
22. A liquid crystal display device according to claim 13, wherein
the light shielding matrix includes chromium.
23. A liquid crystal display device according to claim 13, wherein
the light shielding matrix includes chromium and chromium
oxide.
24. A liquid crystal display device according to claim 13, wherein
the light shielding matrix includes chromium oxide.
25. A liquid crystal display device comprising:
a first substrate and a second substrate;
a liquid crystal layer provided between said first and second
substrates;
a plurality of pixel regions provided on the surface opposing said
second substrate of said first substrate, each of said pixel
regions comprising at least one pixel electrode and a common
electrode cooperatively applying an electric field in a direction
along the surface of said first substrate; and
a conductive light shielding matrix provided on the surface
opposing said first substrate of said second substrate, said light
shielding matrix having openings, each corresponding to a display
region of each of said pixel regions, and shading non-display
regions other than said pixel regions;
wherein a conductive film at substantially the same voltage as said
common electrode is formed at least above said light shielding
matrix with a insulating film interposed therebetween,
wherein said liquid crystal layer is encapsulated between said
first and second substrates by a sealing member, said common
electrode formed on said first substrate is extended outside the
sealing position of said sealing member on said first substrate,
said light shielding matrix formed on said second substrate is
extended outside the sealing position of said sealing member on
said second substrate, and said common electrode and said light
shielding matrix are electrically connected at a position outside
said sealing member via a conductive member provided between said
first and second substrates.
26. A liquid crystal display device according to claim 25, wherein
the common electrode and the pixel electrode are on different
layers.
27. A liquid crystal display device according to claim 25, wherein
the light shielding matrix includes chromium.
28. A liquid crystal display device according to claim 25, wherein
the light shielding matrix includes chromium and chromium
oxide.
29. A liquid crystal display device according to claim 25, wherein
the light shielding matrix includes chromium oxide.
30. A liquid crystal display device according to claim 25, wherein
the conductive film has an opening substantially the same size as
the opening in the light shielding matrix.
31. A liquid crystal display device according to claim 25, wherein
the conductive film includes a transparent layer.
32. A liquid crystal display device according to claim 25, wherein
the conductive film includes an opaque layer.
33. A liquid crystal display device according to claim 25, wherein
the conductive film is in a horizontal direction.
34. A liquid crystal display device according to claim 25, wherein
the conductive film is in a vertical direction.
35. A liquid crystal display device according to claim 25, wherein
the conductive film has a first portion in a first direction and a
second portion in a second direction is in a horizontal
direction.
36. A liquid crystal display device as set forth in claim 25,
wherein the voltage difference between said conductive film and
said common electrode is set in a range of from -0.5 V to +0.5 V,
both inclusive.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device in
which alignment of liquid crystal can be controlled by applying an
electric field along the substrate face, and relates to a structure
in which in addition to a wider angle of view, a higher aperture
ratio can be achieved.
2. Description of the Prior Art
Recent TN mode liquid crystal display devices have a problem of
high dependency on the angle of view, since the visibility in the
vertical direction is inferior in spite of excellent visibility in
the lateral direction. The applicant of this application claimed
liquid crystal display devices having a structure by which the
above problem can be solved in Japanese Patent Application Nos.
7-1579, 7-306276, and the like.
According to the techniques described in such Patent Applications,
instead of providing liquid crystal driving electrodes for each of
the upper and lower substrates sandwiching the liquid crystal
layer, two types of linear electrodes 12 and 13 having different
polarity from each other are provided only on the lower substrate
11 at a distance from each other, as is shown in FIG. 10, and no
electrode is formed on the upper substrate 10 shown in the upper
side of FIG. 10 so that liquid crystal molecules 36 are aligned in
the direction of the transverse electric field (in the
substrate-face direction) which is generated between the linear
electrodes 12 and 13 by applying a voltage.
In more detail, as is shown in FIG. 9, the linear electrodes 12 are
connected by a base line 14 to form a comb-shaped electrode 16, the
linear electrodes 13 are connected by a base line 15 to form a
comb-shaped electrode 17, the comb-shaped electrodes 16 and 17 are
engaged with each other such that the linear electrodes 12 and 13
are alternately positioned without being in contact with each
other, and a switching element 19 and a power source 18 are
connected to the base lines 14 and 15.
As is shown in FIG. 11A, an alignment film is formed on the
liquid-crystal side of the upper substrate 10 to align the liquid
crystal molecules 36 in the .beta. direction, another alignment
film is formed on the liquid-crystal side of the lower substrate 11
to align the liquid crystal molecules 36 in the .gamma. direction
parallel to the .beta. direction, and a polarizing plate polarizing
light in the .beta. direction shown in FIG. 11A and a polarizing
plate polarizing light in the .alpha. direction are provided for
the substrates 10 and 11, respectively.
According to the above structure, the liquid crystal molecules 36
are homogeneously aligned in the same direction when no voltage is
applied between the linear electrodes 12 and 13, as is shown in
FIGS. 11A and 11B. In this state, a light beam transmitted through
the lower substrate 11 is polarized in the .alpha. direction by the
polarizing plate, passes through a layer of the liquid crystal
molecules 36, and then reaches the polarizing plate of the upper
substrate 10, which polarizing plate has a polarization direction
.beta. different from the direction .alpha.. The light beam is
thereby shaded by the polarizing plate of the upper substrate 10
and is unable to pass through the liquid crystal display device,
thereby rendering the liquid crystal display device in a dark
state.
When a voltage is applied between the linear electrodes 12 and 13,
among the liquid crystal molecules 36, those adjacent to the lower
substrate 11 are aligned perpendicular to the longitudinal
direction of the linear electrodes 12 and 13. The nearer a liquid
crystal molecule is located to the lower substrate 11, the more
strongly this phenomenon is observed. In other words, lines of
electric force perpendicular to the longitudinal direction of the
linear electrodes 12 and 13 are generated by the transverse
electric field (an electric field in the substrate-face direction)
produced by the linear electrodes 12 and 13. Thus, the major axes
of the liquid crystal molecules 36 aligned in the .gamma. direction
by the alignment film formed on the lower substrate 11 are altered
to the .alpha. direction, i. e., perpendicular to the .gamma.
direction, by the force of the electric field which is stronger
than that of the alignment film, as is shown in FIG. 12A.
Therefore, twisted alignment is achieved in the liquid crystal
molecules 36 by applying a voltage between the linear electrodes 12
and 13, as is shown in FIGS. 12A and 12B. In this state, the
polarization direction of the polarized light beams, which have
been transmitted through the lower substrate 11 and polarized in
the .alpha. direction, is converted by the twisted liquid crystal
molecules 36 so that the polarized light beams are allowed to pass
through the upper substrate 10 having a polarizing plate whose
polarization direction .beta. is different from the .alpha.
direction. The liquid crystal display device thereby exhibits a
bright state.
FIGS. 13 and 14 are an enlarged fragmentary view of the structure
of an actual active-matrix liquid crystal driving circuit to which
a liquid crystal display device equipped with the linear electrodes
12 and 13 is applied.
The structure shown in FIGS. 13 and 14 corresponds to only one
pixel. On a transparent substrate 20 such as a glass substrate, a
gate electrode 21 and linear common electrodes 22 both made of a
conductive layer are separately provided parallel to each other. A
gate insulating film 24 is formed to cover these electrodes. A
thin-film transistor T is formed such that a source electrode 27
and a drain electrode 28 are formed on a portion of the gate
insulating film 24 corresponding to the gate electrode 21, and a
semiconductor film 26 is provided on a portion of the gate
insulating film 24 between the source electrode 27 and the drain
electrode 28. A linear pixel electrode 29 made of a conductive
layer is formed on a portion of the gate insulating film 24 between
the common electrodes 22.
FIG. 13 is a plan view of these electrode. Gate lines 30 and signal
lines 31 are formed on the transparent substrate 20 according to a
matrix pattern. The gate electrode 21 which is a part of the gate
line 30 is provided at a corner of each pixel region formed by the
gate lines 30 and the signal lines 31. Via a capacitor electrode
33, the drain electrode 28 above the gate electrode 21 is connected
to the pixel electrode 29 which is provided between the common
electrodes 22 in parallel with the signal line 31 and the common
electrodes 22.
The ends, near the gate line 30, of the common electrodes 22 are
connected by a connecting line 34, provided in the pixel region in
parallel with the gate line 30, and the other ends of the common
electrodes 22 are connected by a common line 35, provided in the
pixel region in parallel with the gate line 30. The common line 35
is provided over numerous pixel regions in parallel with the gate
line 30 so as to apply a common voltage to the common electrodes 22
provided for each pixel region.
As is shown in FIG. 14, on the surface, opposing the substrate 20,
of the substrate 37, a light shielding matrix 38 is formed with an
opening 38a corresponding to a pixel region, and a color filter 39
is also provided to cover the opening 38a.
In the above structure shown in FIGS. 13 and 14, lines of electric
force generated by a transverse electric field can be obtained
along the directions of the arrows a shown in FIG. 14. Thus, the
liquid crystal molecules 36 are aligned by the transverse electric
field in a manner shown in FIG. 14. The dark and bright states are
thereby switchable by controlling the alignment of the liquid
crystal molecules 36 similarly to the above description made with
reference to FIGS. 11 and 12.
However, according to liquid crystal display devices having the
above structure, the aperture ratio is disadvantageously reduced in
spite of a wide angle of view. In other words, although the liquid
crystal molecules 36 are aligned by the transverse electric field
generated between the pixel electrode 29 and the common electrodes
22 in the structure shown in FIGS. 13 and 14, in regions above the
common electrodes 22, the direction of the electric field applied
to the liquid crystal molecules 36 differs from that of the
transverse electric field, and thus the alignment direction of the
liquid crystal molecules 36 in the regions above the common
electrodes 22 is different from that in the region between the
pixel electrode 29 and the common electrodes 22, as is shown in
FIG. 10.
Therefore, as is shown in FIG. 14, the light shielding matrix 38 is
conventionally employed for shading the regions above the common
electrodes 22, which regions may cause problems such as light
leakage. Furthermore, the periphery of the opening 38a of the light
shielding matrix 38 is positioned slightly inside the inner end 22a
of each common electrode 22, thereby increasing the region shaded
by the light shielding matrix 38. Thus, the aperture ratio of the
resulting liquid crystal display device cannot be increased.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems, it is an object of the
present invention to provide a liquid crystal display device having
a high aperture ratio while maintaining a wide angle of view, in
which the liquid crystal is driven by a transverse electric
field.
To solve the above object, a liquid crystal display device of the
present invention is composed of: a first substrate and a second
substrate; a liquid crystal layer provided between the first and
second substrates; a plurality of pixel regions provided on the
surface opposing the second substrate of the first substrate, each
of which pixel regions has at least one pixel electrode and a
common electrode cooperatively applying an electric field in a
direction along the surface of the first substrate; and a
conductive light shielding matrix provided on the surface opposing
the first substrate of the second substrate, which light shielding
matrix has openings, each opening corresponding to a display region
of each of the pixel regions, and shades non-display regions other
than the pixel regions; in which the light shielding matrix and the
common electrode are set to substantially the same voltage.
In addition, a liquid crystal display device of the present
invention may be composed of: a first substrate and a second
substrate; a liquid crystal layer provided between the first and
second substrates; a plurality of pixel regions provided on the
surface opposing the second substrate of the first substrate, each
of which pixel regions has at least one pixel electrode and a
common electrode cooperatively applying an electric field in a
direction along the surface of the first substrate; and a
conductive light shielding matrix provided on the surface opposing
the first substrate of the second substrate, which light shielding
matrix has openings, each opening corresponding to a display region
of each of the pixel regions, and shades non-display regions other
than the pixel regions; in which a conductive film at substantially
the same voltage as the common electrode is formed at least above
the light shielding matrix with an insulating film interposed
therebetween, and the light shielding matrix and the common
electrode are set to substantially the same voltage.
According to such structures, a transverse electric field can be
applied to the liquid crystal layer by the common electrode and the
pixel electrode both provided on the substrate, thereby switching a
dark state and a bright state. In addition, since the common
electrode and the light shielding matrix or the conductive layer
are set to substantially the same voltage, the lines of electric
force of the transverse electric field applied to liquid crystal
molecules near the common electrode can be uniform. Thus, alignment
disorder of the liquid crystal molecules in a region near the
common electrode can be reduced, the liquid crystal molecules in
that region can be used for displaying, and thus the region is not
required to be shaded by the light shielding matrix. The light
shielding matrix is thereby allowed to have larger openings as
compared with those in the prior art, resulting in an improved
aperture ratio.
In the above liquid crystal display device, the voltage difference
is preferably set in a range of from -0.5 V, to +0.5 V, both
inclusive.
When the voltage difference between the common electrode and the
light shielding matrix is outside the above range, the lines of
electric force applied to the liquid crystal in the region
corresponding to the common electrode are disturbed so that the
alignment disorder of the liquid crystal molecules 36 is readily
increased and causes problems such as light leakage. Thus, it
becomes impossible to enlarge the opening of the light shielding
matrix and to improve the aperture ratio.
Furthermore, a liquid crystal display device of the present
invention may have the following structure: the common electrode
formed on the first substrate is extended to a peripheral edge of
the first substrate, the light shielding matrix or the conductive
film formed on the second substrate is extended to a peripheral
edge of the second substrate, and the common electrode and the
light shielding matrix or the conductive film are electrically
connected via a conductive member at the peripheral edge of the
first and second substrates.
Moreover, a liquid crystal display device of the present invention
may have the following structure: the liquid crystal layer is
encapsulated between the first and second substrates by a sealing
member, the common electrode formed on the first substrate is
extended outside the sealing position of the sealing member on the
first substrate, the light shielding matrix or the conductive film
formed on the second substrate is extended outside the sealing
position of the sealing member on the second substrate, and the
common electrode and the light shielding matrix or the conductive
film are electrically connected at a position outside the sealing
member via a conductive member provided between the first and
second substrates.
According to the above structures, the common electrode and the
light shielding matrix or the conductive film can be readily
connected electrically at substantially the same voltage, thereby
achieving a liquid crystal cell having a wide angle of view and a
high aperture ratio.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary cross-sectional view showing a liquid
crystal display device of the first embodiment incorporated in the
present invention;
FIG. 2 is a plan view showing an arrangement of electrodes in the
first embodiment;
FIG. 3 is a perspective view showing a light shielding matrix and a
substrate surface in the first embodiment;
FIG. 4 is a fragmentary cross-sectional view showing the structure
of a connection portion at a peripheral edge of the substrates in
the first embodiment;
FIG. 5 is a fragmentary cross-sectional view showing a liquid
crystal display device of the second embodiment incorporated in the
present invention;
FIG. 6A shows the simulation results obtained from a liquid crystal
display device of Example in which a light shielding matrix and
common electrodes are connected and grounded, and FIG. 6B shows the
simulation results obtained from a liquid crystal display device of
Comparative Example in which a light shielding matrix and common
electrodes are not connected, the light shielding matrix is
floating, and the common electrodes are grounded;
FIG. 7A is a photograph showing the result of a light-leakage
occurrence test using a liquid crystal display device of Example in
which a light shielding matrix and common electrodes are connected
and grounded, and FIG. 7B is a photograph showing the result of a
light-leakage occurrence test using a liquid crystal display device
of Comparative Example in which the gate electrode voltage V.sub.G
is set to 15 V, a light shielding matrix is floating, and common
electrodes are grounded;
FIGS. 8A and 8B show the transmittance-driving voltage
characteristics of the liquid crystal display devices of Example
and Comparative Example, respectively;
FIG. 9 is a plan view of a substrate, having linear electrodes
thereon, of a liquid crystal display device of the prior art, in
which device alignment of liquid crystal molecules is controlled by
applying a transverse electric field;
FIG. 10 shows alignment of liquid crystal molecules when a voltage
is applied to the linear electrodes shown in FIG. 9;
FIG. 11A shows alignment of liquid crystal molecules in a dark
state of a liquid crystal display device of the prior art, in which
device alignment of the liquid crystal molecules is controlled by
applying a transverse electric field, and FIG. 11B is a side view
of the alignment shown in FIG. 11A;
FIG. 12A shows alignment of liquid crystal molecules in a bright
state of a liquid crystal display device of the prior art, in which
device alignment of the liquid crystal molecules is controlled by
applying a transverse electric field, and FIG. 12B is a side view
of the alignment shown in FIG. 12A;
FIG. 13 is a plan view showing linear electrodes in a liquid
crystal display device of the prior art, in which device alignment
of liquid crystal molecules is controlled by applying a transverse
electric field;
FIG. 14 shows the cross-sectional structure of the liquid crystal
display device shown in FIG. 13;
FIG. 15A shows the relationship between the reduction in the
transmittance and the voltage difference between the light
shielding matrix and the common electrodes in a liquid crystal
display device of Example, with the transmittance obtained by
setting the light shielding matrix and the common electrodes to the
same voltage being defined as 100% transmittance;
FIG. 16 shows a structural example incorporated in the present
invention;
FIG. 17 shows another structural example incorporated in the
present invention; and
FIG. 18 shows still another structural example incorporated in the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be better understood from the following
description of the preferred embodiments taken in conjunction with
the accompanying drawings.
FIGS. 1 to 4 show main sections of a liquid crystal display device
of the first embodiment incorporated in the present invention. In
FIG. 1, an upper substrate (second substrate) 40 and a lower
substrate (first substrate) 41 are positioned opposing each other
with a predetermined space (cell gap) therebetween, a liquid
crystal layer 42 is formed between the substrates 40 and 41, and
polarizing plates 43 and 44 are provided on the outer surface of
the substrates 40 and 41, respectively.
These substrates 40 and 41 are made of a transparent material such
as glass. For actually preparing the above structure, the periphery
of the substrates 40 and 41 is sealed by a sealing member, and a
space formed by the substrates 40 and 41 and the sealing member is
filled with a liquid crystal to form the liquid crystal layer 42. A
liquid crystal cell 45 is obtained by assembling the substrates 40
and 41 and the polarizing plates 43 and 44.
As is shown in FIG. 2, on the transparent substrate 41, a plurality
of gate lines 50 and signal lines 51 are formed according to a
matrix pattern, and linear electrodes (common electrodes) 53 and
another linear electrode (pixel electrode) 54 are provided in
parallel with each other in each pixel region 59 formed by the gate
lines 50 and the signal lines 51.
In more detail, on the substrate 41, a plurality of gate lines 50
are formed in parallel with each other at predetermined intervals;
common lines 56 are provided along the gate lines 50 on the same
plane as that of the gate lines 50; in each region formed by the
gate lines 50 and the signal lines 51, two linear common electrodes
53 are extended from the common line 56 in a perpendicular
direction to the common line 56; near an adjacent gate line 50, the
ends of the two common electrodes 53 are connected by a connecting
line 57; and each region formed by the gate lines 50 and the signal
lines 51 is used as the pixel region 59.
Although, numerous pixel regions 59 required for a liquid crystal
display device are provided in the liquid crystal cell 45 as a
whole, FIG. 1 shows a fragmentary cross-sectional structure of one
pixel region 59 and FIG. 2 shows a plan structure corresponding to
two adjacent pixel regions 59.
Each of the thin-film transistors (switching elements) T.sub.1
shown in FIG. 2 is formed as follows: an insulating layer 58
covering the above-mentioned lines is formed on the substrate 41,
as is shown in FIG. 1; the gate lines 50 and the signal lines 51
are formed on the insulating layer 58 such that each of the gate
line 50 and the signal lines 51 perpendicularly cross each other to
form a matrix pattern on the plan view; a portion of the gate line
50 near an intersection between the gate line 50 and a signal line
51 is used as the gate electrode 60; and a source electrode 62 and
a drain electrode 63, between which a semiconductor film 61 is
formed, are provided on a portion of the insulating layer 58 above
the gate electrode 60. In the center of each pixel region 59, a
linear pixel electrode 54 is provided in parallel with the common
electrodes 53. A capacitance generating section 65 is formed by
extending one end of the pixel electrode 54 on a portion of the
insulating layer 58 above the common line 56 and another
capacitance generating section 66 is formed by extending the other
end of the pixel electrode 54 on a portion of the insulating layer
58 above the connecting line 57. The capacitance generating
sections 65 and 66 are provided for generating capacitance between
the insulating layer 58 and the common line 56 or the connecting
line 57 so as to cancel the parasitic capacitance at the time of
driving the liquid crystal.
The source electrode 62 is connected to the signal line 51, the
drain electrode 63 is connected to the capacitance generating
section 66 formed on the portion of the insulating layer 58 above
the connecting line 57, and they are covered with an alignment film
67, as is shown in FIGS. 1 and 2.
The electrodes 53 and 54 used for the above first embodiment may be
formed as either a light-shading metallic electrode or a
transparent electrode. However, in the case of employing the
undermentioned normally black mode display, transparent electrodes
made of ITO (indium tin oxide), etc. are preferable.
On the lower surface of the substrate 40, a light shielding matrix
71 is formed with an opening 70 corresponding to the pixel region
59 formed on the substrate 41, and a color filter 72 is also
provided to cover the opening 70. An alignment film 73 covering the
light shielding matrix 71 and the color filter 72 is also formed.
The light shielding matrix 71 is made of a light-shading metallic
film composed of a Cr layer alone or composed of a CrO layer and a
Cr layer, and is used for shading non-display portions of each
pixel region 59 such that it shades the common line 56, the
connecting line 57, the signal line 51, and the gate line 50 in
each pixel region 59 and it also shades a part of the common
electrode 53 in the width direction. In other words, as is shown by
the dotted chain lines of FIG. 2, substantially the entire region
between the common electrodes 53 of each pixel region 59 and almost
the common electrodes 53 as a whole in the width direction are
exposed by the opening 70 of the light shielding matrix 71.
In the case of a color liquid crystal display device, color filters
72 (red, green, and blue) are provided for pixel regions 59, as is
shown in FIG. 1. However, the color filters 72 can be omitted in
monochrome liquid crystal display devices.
The periphery of the light shielding matrix 71 formed on the
substrate 40 is extended outside the sealing member 75 provided on
the periphery of the substrate 40 for sealing the liquid crystal,
as is shown in FIG. 4. The common lines 56 formed on the substrate
41 are extended outside the sealing member 75 provided on the
periphery of the substrate 41 for sealing the liquid crystal, as is
shown in FIGS. 3 and 4. As is shown in FIG. 4, terminals 56a
connecting to the common lines 56 are provided on the periphery of
the substrate 41 and connected to the light shielding matrix 71 by
a conductive member 76 such as an Ag paste provided between the
substrates 40 and 41 so that the light shielding matrix 71 and the
common lines 56 (common electrodes 53) have the same voltage
(ground voltage). Two terminals 56a are employed in the first
embodiment so as to ensure the connection between one terminal and
the light shielding matrix 71 via the conductive member 76 even
when the connection between the other terminal 56a and the light
shielding matrix 71 is damaged.
In the first embodiment, the light shielding matrix 71 and the
common lines 56 (common electrodes 53) are connected to the same
voltage, however, they may be substantially at the same voltage and
are not required to be at completely the same voltage.
"Substantially the same voltage" is defined as follows: the voltage
difference between the light shielding matrix 71 and the common
electrodes 53 is in a range of from -0.5 V to +0.5 V, both
inclusive.
In the liquid crystal display device of the first embodiment, the
alignment film 73 of the substrate 40 and the alignment film 67 of
the substrate 41 are aligned in a direction substantially parallel
to the longitudinal direction of the common electrodes 53. The
liquid crystal molecules in the liquid crystal layer 42 interposed
between the substrates 40 and 41 are thereby homogeneously aligned
such that the major axis of the liquid crystal molecules is in
parallel with the longitudinal direction of the common electrodes
53 without an applied electric field.
Furthermore, in the structure of the first embodiment, the
polarization axis of the polarizing plate 43 is in a direction
substantially parallel to the longitudinal direction (the
sheet-thickness direction of FIG. 1) of the common electrodes 53,
and the polarization axis of the polarizing plate 44 is in a
direction substantially perpendicular to the longitudinal direction
(the lateral direction of FIG. 1).
According to the above structure incorporated in the present
invention, the dark state and the bright state can be switched by
switching the application of a voltage between the common
electrodes 53 and pixel electrode 54 that are in the desired pixel
regions 59 using the thin-film transistor T.sub.1, i. e., a
switching element.
In other words, when a voltage is applied between the common
electrodes 53 and pixel electrodes 54 that are in the desired pixel
regions 59 by operating the thin-film transistor T.sub.1, an
electric field is generated in the transverse direction of FIG. 1
and is applied to the liquid crystal layer. The liquid crystal
molecules are thereby twisted between the substrates 40 and 41,
resulting in a bright state similarly to FIG. 12.
With no applied voltage between the common electrodes 53 and pixel
electrodes 54, the liquid crystal molecules are homogeneously
orientated in the same direction as the alignment direction of the
alignment films 67 and 73, resulting in a dark state similarly to
FIG. 11.
The alignment of the liquid crystal molecules is controlled as
mentioned above. Thus, the light beams, which emerge from a back
light provided below the substrate 41, are shaded or transmitted
according to the alignment of the liquid crystal molecules. In this
case, the display is in the so-called normally black mode such that
the display is in the dark state without controlling the alignment
of the liquid crystal molecules and is in the bright state when the
alignment of the liquid crystal molecules is controlled. Since the
liquid crystal molecules 36 are aligned homogeneously along the
substrate-face direction or twisted by 90.degree. between the
substrates 40 and 41, the resulting liquid crystal display device
has a wide angle of view and a small dependency of transmittance on
the angle of view.
According to the structure of the first embodiment, it is possible
to set the light shielding matrix 71 and the common electrodes 53
at substantially the same voltage. Thus, the disturbance of the
lines of electric force in regions corresponding to the common
electrodes 53 can be reduced, and as a result, alignment disorder
of the liquid crystal molecules can be decreased. In other words,
in the structure shown in FIG. 14, since the light shielding matrix
38 is electrically floating, it may be affected by a surrounding
electric field and have a variable voltage. Thus, the liquid
crystal alignment in the regions corresponding to the common
electrodes 22 may be disturbed by the voltage generated in the
light shielding matrix 38. However, according to the structure of
the first embodiment incorporated in the present invention, the
light shielding matrix 71 and the common electrodes 53 are grounded
at substantially the same voltage. Thus, the disturbance of the
electric field in the regions corresponding to the common
electrodes 53 is reduced, and the alignment of the liquid crystal
molecules in the regions corresponding to the common electrodes 53
is improved as compared with conventional structures. As a result,
problems such as light leakage in the regions corresponding to the
common electrodes 53 do not readily occur. Therefore, the opening
70 of the light shielding matrix 71 can also be extended to the
region (the region above the common electrodes 53) in which light
leakage does not occur, resulting in a liquid crystal display
device having a high aperture ratio.
Therefore, the dark state and the bright state can be switched
according to the liquid crystal alignment controlled by applying a
transverse electric field, thereby providing a liquid crystal
display device having a high aperture ratio and small dependency on
the angle of view.
In the structure of the first embodiment, "substantially the same
voltage" means preferably as follows: the voltage difference
between the light shielding matrix 71 and the common electrodes 53
is set in a range of from -0.5 V to +0.5 V, both inclusive.
When the voltage difference between the light shielding matrix 71
and the common electrodes 53 is outside the above range, the lines
of electric force applied to the liquid crystal in the regions
corresponding to the common electrodes 53 are disturbed so that the
alignment disorder of the liquid crystal molecules is readily
increased and causes problems such as light leakage. Thus, it
becomes impossible to enlarge the opening 70 of the light shielding
matrix 71 and to improve the aperture ratio.
Furthermore, the driving voltage for obtaining the maximum
transmittance as a liquid crystal display device can be reduced in
the structure of the first embodiment, because the aperture ratio
is improved by the enlargement of the opening 70 of the light
shielding matrix 71, which enlargement is achieved by reducing the
alignment disorder of the liquid crystal molecules 36 in the
regions corresponding to the common electrodes 53.
The parasitic capacitance generated in the liquid crystal display
device can be partially canceled by a capacitance formed between
the capacitance generating sections 65 and 66 and the common and
connecting lines 56 and 57, both of which oppose the capacitance
generating sections 65 and 66 with the insulating layer 58
interposed therebetween.
FIG. 5 shows a main section of a liquid crystal display device of
the second embodiment, the reference numerals in FIG. 5 identify
substantially identical parts in the first embodiment shown in FIG.
1, and detailed explanations thereof are omitted.
The liquid crystal display device of the second embodiment is
different from that of the first embodiment in the following
aspects: an insulating film 80, such as an over-coat layer,
covering the light shielding matrix 71 and the color filter 72 is
formed on the lower surface (opposing surface) of the substrate 40;
on the insulating film 80, a conductive film 81 is provided with
the same pattern as that of the light shielding matrix 71; and the
alignment film 73 is formed on the conductive film 81.
Furthermore, according to the second embodiment, the common
electrodes 53 and the conductive film 81 are connected by a
conductive member 76', and are grounded at substantially the same
voltage. The conductive film 81 has an opening 82 with the same
pattern as the opening 72 of the light shielding matrix 71.
The conductive layer 81 may be either a shading metallic layer made
of Cr, etc. or a transparent conductive layer made of ITO, etc.
In the liquid crystal display device having the structure shown in
FIG. 5, the dark state and the bright state are switchable by
switching the application of a voltage between the common
electrodes 53 and pixel electrodes 54 that are in the desired pixel
regions 59 using the thin-film transistor T.sub.1 similarly to the
first embodiment.
Since the conductive film 81 and the common electrodes 53 are
allowed to be at substantially the same voltage, the lines of
electric force in the regions corresponding to the common
electrodes 53 are less disturbed so that the alignment disorder of
the liquid crystal molecules can be decreased.
Therefore, as is similar to the liquid crystal display device of
the first embodiment, the opening 70 of the light shielding matrix
71 can be enlarged, and the dark state and the bright state are
switchable according to the liquid crystal alignment controlled by
a transverse electric field, thereby providing a liquid crystal
display device having a high aperture ratio and small dependency on
the angle of view.
Furthermore, in the liquid crystal display device of the second
embodiment, the conductive layer 81 can be positioned nearer to the
liquid crystal molecules as compared with the light shielding
matrix 71. Thus, disturbance of the lines of electric force can be
further reduced as compared with the first embodiment and the
alignment disorder of the liquid crystal in the regions
corresponding to the common electrodes 53 is further decreased.
When a shading metallic layer is employed as the conductive film 81
in the second embodiment shown in FIG. 5, the light shielding
matrix 71 may be omitted. In such a case, the shading metallic
layer is also used as the light shielding matrix 71.
With the light shielding matrix 71 formed on the substrate 40, the
disturbance of the lines of electric force applied to the region
corresponding to the common electrodes 53 can be reduced even if
the conductive film 81 is formed only on the periphery of the
opening 70 of the light shielding matrix 71. Thus, the conductive
film 81 is not required to have completely the same pattern as the
light shielding matrix 71. From the viewpoint of designing, it is
easiest to form the conductive film 81 and the light shielding
matrix 71 with the same pattern, however, the object of the present
invention can be achieved as long as the shape of the conductive
film 81 corresponds to the periphery of the opening 70 of the light
shielding matrix 71.
EXAMPLE AND COMPARATIVE EXAMPLE
A thin-film-transistor-type liquid crystal display device having a
structure shown in FIGS. 1 and 2 was produced as Example.
Two transparent glass substrates 1 mm thick were employed. A
thin-film transistor circuit having the linear electrodes was
formed on one substrate (first substrate). An alignment film was
formed on the thin-film transistor circuit and another alignment
film was provided on the other substrate (second substrate). For
aligning liquid crystal, the alignment films were rubbed by a
rubbing roll in parallel with the longitudinal direction of the
linear electrodes. The first and second substrates were positioned
opposing each other at a predetermined distance with gap-forming
beads interposed therebetween. A liquid crystal was poured into the
space formed between the substrates. The first and second
substrates were joined to each other using a sealing member and
assembled into a liquid crystal cell by providing polarizing plates
outside the substrates.
In more detail, this device was prepared as follows: The pitch of
the pixel region was 43 .mu.m for the horizontal direction
(signal-line direction) and 129 .mu.m for the vertical direction
(gate-line direction); the light shielding matrix was made of Cr,
0.3 .mu.m thick, and had 27 .mu.m by 111 .mu.m openings each for a
pixel region. The width of the pixel electrode and the common
electrode was set to 5 .mu.m, and the distance between the pixel
electrode and the common electrode was set to 10 .mu.m.
Thin-film transistors, in each of which a semiconductor film made
of a-Si was formed between a gate electrode and a source electrode,
were provided each near an intersection between the gate line and
the signal line, and covered with an insulating film and a
polyimide alignment film in that order. The alignment film was
rubbed to complete a thin-film transistor array on the first
substrate. The first substrate and the second substrate having a
light shielding matrix, color filters, and a polyimide alignment
film thereon were positioned opposing each other with a 4-.mu.m gap
therebetween. A liquid crystal was encapsulated between the
substrates using a sealing member. Two terminals connecting to the
portion of the light shielding matrix extended to the peripheral
edge of the second substrate outside the sealing member and other
two terminals connecting to the common electrodes were connected by
an Ag paste so as to complete a liquid crystal display device. In
this structure, the light shielding matrix and the common
electrodes were grounded.
As Comparative Example, another liquid crystal display device was
prepared in which the terminals connecting to the light shielding
matrix and those connecting to the common electrodes were not
connected such that the light shielding matrix was electrically
floating and the common electrodes were grounded.
FIGS. 6A and 6B show the simulation results of the lines of
electric force generated by the pixel electrodes and the common
electrodes in the above-mentioned liquid crystal display
devices.
FIG. 6A shows the simulation results obtained from the liquid
crystal display device of Example in which the light shielding
matrix and the common electrodes are connected and grounded, and
FIG. 6B shows the simulation results obtained from the liquid
crystal display device of Comparative Example in which the light
shielding matrix and the common electrodes are not connected, the
light shielding matrix was floating, and the common electrodes were
grounded.
In the lines of electric force shown in FIG. 6A, the rising section
R of the lines of electric force is located outside the ends P of
the region positioned between both common electrodes 53, however,
in the lines of electric force shown in FIG. 6B, the rising section
R' of the lines of electric force is located inside the ends P' of
the region positioned between both common electrodes 53, which fact
indicates that in a structure having the lines of electric force
shown in FIG. 6B, light leakage may occur in the region between
both common electrodes 53, however, in a structure having the lines
of electric force shown in FIG. 6A, light leakage does not readily
occur in the region between both common electrodes 53.
FIG. 7A is a photograph showing the result of a light-leakage
occurrence test using a liquid crystal display device having the
same structure as Example in which the light shielding matrix and
the common electrodes are connected and grounded. The gate
electrode voltage V.sub.G at the time of driving the liquid crystal
display device was set to 15 V, and the common voltage and the
light-shielding-matrix voltage were set to 0 V, i. e., they were
grounded. Light leakage does not occur in this structure, as is
shown in FIG. 7A.
FIG. 7B is a photograph showing the result of a light-leakage
occurrence test using a liquid crystal display device of
Comparative Example in which the gate electrode voltage V.sub.G is
set to 15 V, the light shielding matrix is floating, and the common
electrodes are grounded. As is shown in FIG. 7B, light leakage
occurs in this structure.
From the result shown in FIG. 7B, it is understood that in the
liquid crystal display device of Comparative Example in which the
light shielding matrix is floating and the common electrodes are
grounded, light leakage occurs if the light shielding matrix has
the above-described shape. Thus, it is necessary to extend the area
shaded by the light shielding matrix, undesirably resulting in a
reduction in the aperture ratio.
FIGS. 8A and 8B show the transmittance-driving voltage
characteristics of the liquid crystal display devices of Example
and Comparative Example, respectively.
As is apparent from FIGS. 8A and 8B, the maximum transmittance of
the liquid crystal display device of Example and that of the liquid
crystal display device of Comparative Example are almost the same.
The driving voltage required for obtaining the maximum
transmittance is 6.7 V for the liquid crystal display device of
Example and 7.9 V for the liquid crystal display device of
Comparative Example. Thus, to achieve the same transmittance, the
driving voltage of the liquid crystal display device of Example is
lower than that of the liquid crystal display device of Comparative
Example. As a result, the driving voltage can be reduced by 1.2 V
by employing the liquid crystal display device of Example.
FIG. 15 shows the relationship between the reduction in the
transmittance and the voltage difference between the light
shielding matrix and the common electrodes in the liquid crystal
display device of Example. In FIG. 15, the transmittance obtained
by setting the light shielding matrix and the common electrodes to
the same voltage is defined as 100% transmittance.
As is apparent from FIG. 15, the reduction in the transmittance is
more than 5% when the voltage difference between the light
shielding matrix and the common electrodes exceeds 0.5 V.
Therefore, to obtain a sufficient voltage difference, it is
effective to set the voltage difference between the light shielding
matrix and the common electrodes in a range of from +0.5 V to -0.5
V, both inclusive.
FIGS. 16 to 18 show other examples in which the conductive films 81
at substantially the same voltage as the common electrodes are
partially provided above the light shielding matrix 71.
According to the structure shown in FIG. 16, the strip-shaped
conductive films 81 are provided in the horizontal direction such
that they sandwich the top and bottom sides of the openings 70,
each opening corresponding to a pixel region. In the structure
shown in FIG. 17, the strip-shaped conductive films 81 are provided
in the vertical direction such that they sandwich the right and
left sides of the openings 70, each opening corresponding to a
pixel region. In the structure shown in FIG. 18, the strip-shaped
conductive films 81 are provided in both the horizontal direction
and the vertical direction such that they sandwich the entire right
and left sides and approximately a half of the top and bottom sides
of the openings 70, each opening corresponding to a pixel
region.
In the above structures of FIGS. 16 to 18, similar effects to those
obtained in the structure which is described above with reference
to FIG. 5 can be obtained.
As is mentioned above, according to the present invention, a light
shielding matrix and common electrodes are set to substantially the
same voltage in a liquid crystal display device in which liquid
crystal alignment is controlled by applying a transverse electric
field in a direction parallel to the substrate using the common
electrodes and pixel electrodes. Disturbance of the lines of
electric force applied to the liquid crystal in regions
corresponding to the common electrodes can be thereby reduced and
the liquid crystal in those regions can be used for displaying.
Thus, it becomes unnecessary to shade the regions corresponding to
the common electrodes by the light shielding matrix, a fact which
allows the light shielding matrix to have wider openings as
compared with conventional cases. The resulting liquid crystal
display device achieves higher aperture ratio as compared with
those having conventional structures in which the light shielding
matrix is electrically floating.
Therefore, a liquid crystal display device having a high aperture
ratio and a wider angle of view can be provided, in which the dark
and bright states are switched according to the liquid-crystal
alignment which is controlled by the application of a transverse
electric field.
Furthermore, since the aperture ratio can be improved by enlarging
the openings of the light shielding matrix by reducing the
alignment disorder of the liquid crystal in regions corresponding
to the common electrodes, the driving voltage required to obtain
the maximum transmittance can be decreased, which fact means that
the liquid crystal display device can be driven using less electric
power.
The above structure can also be applied to a structure in which a
conductive film having the same shape as that of the light
shielding matrix is formed on the light shielding matrix with an
insulating film therebetween. In such a case, similar effects to
the above structure can be obtained by connecting the conductive
film and the common electrode to substantially the same voltage.
"Substantially the same voltage" means that the voltage difference
between the conductive film and the common electrodes is set in a
range of from -0.5 V to +0.5 V, both inclusive. When the voltage
difference is in the above range, the above effects can be
ensured.
For reliably setting the common electrodes and the light shielding
matrix or the conductive film to substantially the same voltage,
connecting terminals of the common electrodes and the light
shielding matrix or the conductive film may be extended to the
peripheral edges of the substrates, on which the common electrodes
and the light shielding matrix or the conductive film are formed,
and be connected to each other by a conductive member such as a
conductive paste.
In addition, for reliably setting the common electrodes and the
light shielding matrix or the conductive film to substantially the
same voltage, the common electrodes and the light shielding matrix
or the conductive film may be partially extended outside the
sealing member, encapsulating liquid crystal between the
substrates, so as to be connected to each other by a conductive
member such as a conductive paste.
* * * * *